1. Field
One embodiment of the invention relates to technology for protecting contents recorded on recordable storage media, and in particular to an information processing apparatus, authentication method, and a storage medium for revocating illegal or invalid apparatuses and illegal or invalid media.
2. Description of the Related Art
There is a memory card called a secure digital (SD) Memory card as an example of content storage media. An SD Memory Card adopts a content protection technology called content protection for recordable media (CPRM). The CPRM uses the following technology.
A mutual authentication system is adopted as a scheme for reading/writing management information, such as a cipher key used for encrypting contents for protection, from/to a memory card. Further, as a scheme for revocating an illegal apparatus, technology using key management information called a media key block is adopted (see Content Protection for Recordable Media Specification: SD Memory Card Book Common Part, Revision 0.961, May 3, 2007). An illegal apparatus removes protective information which has been added to contents by a content protection technology, falsifies contents, or discloses confidential information thereof.
Key management information is issued by a technology license organization. Key management information disables decryption of an encrypted content stored in a storage medium such as a memory card by an apparatus recognized as an illegal apparatus when the license is issued (invalidation or exclusion of an illegal apparatus, which is sometimes called revoke). Key management information includes two or more encrypted media keys obtained by encrypting a specific media key by two or more different device keys. A media key is key information used for encryption of a cipher key itself for authentication or encryption of a storage medium and both apparatuses used for communication. A device key is key information assigned uniquely or constantly to each storage medium and each apparatus. At least one device key is stored in a storage medium or apparatus. If key management information invalidating the media key is newly generated and used for authentication of an illegal apparatus, authentication of an illegal apparatus fails. As a result, an illegal apparatus can be disabled or excluded. Therefore, key management information must be the latest reflecting information about an illegal apparatus known when the storage medium is manufactured. If not, robust and efficient invalidation of an illegal apparatus is impossible. Therefore, a memory card adopts a scheme to update key management information.
Unlike a magnetic disc and an optical disc such as a digital versatile disc (DVD), a memory card itself includes a controller in addition to a flash memory for storing data. The controller is used for mutual authentication between a memory card and an information processing apparatus, to prevent reading or writing of data such as a cipher key and key management information by an illegal apparatus.
On the other hand, in a key management method which protects copyright of contents by recording and storing contents on recording media having a secret area, a method of encrypting a content by a title key to prevent wasteful use of a secret area has been proposed (Jpn. Pat. Appln. KOKAI Publication No. 2006-217218).
A method of mutual authentication for ensuring the safety of copyright protection technology has also been proposed (Jpn. Pat. Appln. KOKAI Publication No. 2004-220317).
When key management information in a memory card is updated, it is necessary to re-encrypt and rewrite a title key in a protected area of a memory card by using a media unique key specific to a memory card derived from the key management information. There are many title keys (e.g., several thousands), and if a user removes a memory card from an apparatus while re-encrypted title keys are being written in a protected area, re-encryption of all title keys is not completed, some title keys are encrypted by an old media unique key, not all title keys are normally encrypted, and the contents may not be decrypted.
The above problem in an SD Memory Card occurs in other memory cards.